The Bearing Capacity of Debris Flows

by Luis E. Vallejo, Univ of Pittsburgh, Pittsburgh, United States,
Hankyu Yoo, Univ of Pittsburgh, Pittsburgh, United States,

Abstract: Debris flows are made of a cohesive muddy matrix in which large and heavy particles exist in suspension. To explain how these particles are maintained in suspension, several mechanisms have been put forward. These mechanisms consider the effect of the cohesive strength and the buoyancy offered by the cohesive matrix, the pore water pressures in the void spaces of the muddy matrix, the dispersive pressure between the large grains, and the effect of turbulence. In debris flows, the large particles in suspension are subjected to random and violent movement during the flows. Thus, the large particles will exert loads on the muddy matrix at high strain rates. It is known that high rates of application of loads to solid samples of clay result in an increase in their compressive strength. Therefore, the objective of this study was to investigate if high rates of loading of muds by a sphere (that simulates a large particle in a debris flow) had an influence on the bearing capacity of muds forming part of debris flows. From a laboratory investigation, it was found that the higher the rate of loading of the mud by a sphere, the higher is the bearing capacity of the mud. Thus, the rate of loading of the muddy matrix by the particles in debris flows seems to be an additional mechanism that needs to be taken into consideration when explaining the capacity of debris flows to transport large particles in suspension.

Subject Headings: Mud | Solids flow | Particles | Debris | Load bearing capacity | Matrix (mathematics) | Loading rates

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